Police are investigating the deaths of two Melbourne housemates who used suicide equipment provided by euthanasia advocate Philip Nitschke.

Viewbank housemates Val Seeger, 75, and Claire Parsons, 66, died in March in a suicide pact.

Ms Parsons, who was healthy, had agreed to help carry out her friend's wish to die after she began showing early signs of dementia, Dr Nitschke said.

Dr Philip Nitschke, the director of pro-euthanasia group Exit International, said the deaths were in a "murky" area between suicide and euthanasia. Photo: Kate Geraghty

Laws prohibiting assisting a suicide, and the thought of living on without her best friend, had spurred Ms Parson's decision to also die, he said.

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"Claire said she couldn't live with the risk of criminal charges for assisting suicide ... and she said Val is my closest friend and I don't really want to go on without her," Dr Nitschke said.

The pair, who had been friends for more than two decades, had sent a letter to Dr Nitschke saying they had decided to take their own lives, and asked that it be circulated.

Heidelberg police this week questioned Dr Nitschke over the deaths.

Dr Nitschke said he has admitted providing the equipment, which is legal, but can be used for suicide.

"I've answered all their questions," he said.

Fairfax Media has obtained a copy of a letter written by Ms Parsons before her death.

In the letter, Ms Parsons says her friend was suffering from the onset of Alzheimer’s disease and due to her background as a health professional sought to avoid an ‘‘undignified end’’.

She also outlined why she decided to join Ms Seeger in taking her own life.

‘‘Under the current (and we believe outdated) law in this land, the police are obliged to charge me with aiding and abetting a suicide and I am not prepared to undergo the harassment and disgrace of a prosecution,’’ the letter reads.

‘‘This leaves me no choice but to join my friend at her time of death.’’

The maximum penalty for assisting suicide in Victoria is five years' jail, but in other jurisdictions it is life imprisonment.

Dr Nitschke, the director of pro-euthanasia group Exit International, said the deaths were in a "murky" area between suicide and euthanasia.

He said prosecutors in the UK were able to consider compassionate circumstances in cases of assisted suicide.

"I think there needs to be a look at ways of dealing with these compassionate acts ... when someone feels obliged to help someone they love or care a great deal about then they shouldn't find themselves subjected to these penalties."

Dr Nitschke said the two women were prominent Victorians – Ms Parsons was a renowned medical anthropology academic and published author, and Ms Seeger a highly respected nurse.

The two women were members of their local Exit International group.

Dr Nitschke said the women had spoken about their suicide pact at their last Exit International meeting.

A Victoria Police spokesman said police investigate all unsuspected deaths for the Coroner.

"If a death is deemed non-suspicious, then a brief is prepared for the Coroner," he said.

"The Coroner may direct police to investigate further or may make a finding based on the available evidence."

For help or information call Suicide Helpline Victoria on 1300 651 251 or Lifeline on 131 114, or visit beyondblue.org.au